1. Field of the Invention
The present invention relates to an improved container for the vacuum evaporation of metal which is made of a conductive ceramic. More particularly, it relates to a container for the evaporation of metal which has excellent wettability to molten metal and which enables the use of a high evaporation speed.
2. Description of the Prior Art
Heretofore, containers used for the evaporation of metal have been made of a metal having a high melting point, such as tungsten (W), tantalum (Ta), molybdenum (Mo) and the like. These containers, typically of the boat type, have excellent wettability to molten metals but are easily corroded and are difficult to use repeatedly. Additionally, containers of the vacuum evaporation of metal can be made of an electrically conductive ceramic of TiB.sub.2, ZrB.sub.2 and the like, which is highly anticorrosive and conductive. The containers are superior to the metallic containers since they can be repeatedly used. However, they suffer from a serious disadvantage in that they possess inferior wettability to molten metal.
In vacuum evaporation, a molten metal is primarily heated by thermal conduction from the surface of the container. Consequently, if the container is not wettable to molten metal, the surface of the container will not be substantially wetted by the molten metal and low thermal conduction will result. Accordingly, it takes a correspondingly longer time to reach a sufficiently high temperature for the molten metal and fast evaporation rates cannot be achieved. Consequently, it would be most desirable to have a material for a container, used to evaporate metal, which is both highly anticorrosive and which maintains high wettability to the molten metal.